Leak detectors are known from publications DE-C2 31 24 205, DE-A1 42 28 313 and DE-A1 195 23 430. These are counterflow leak detectors which are commonly operated with helium as the test gas. During leak detection operation, the gas which in the instance of a defective device under test contains the test gas, flows through a line from the inlet of the leak detector to the backing pump. This line is connected through line sections to at least the outlet area of the high-vacuum pump, preferably also with a pressure stage. Depending on which of the line sections is open, leak detection is performed at a different sensitivities.
Generally there exists the problem where in the instance of leak detectors of this kind the response time, i.e. the time which elapses from the point of time when the test gas enters into the inlet of the leak detector until the point of time when the test gas is recorded, is relatively long and specifically so at higher pressures. From EP-B1 752 095 a leak detector is known where its inlet is connected via a test gas line to a gas supply pump. For the connection of the test gas line to the outlet area of the high-vacuum pump, a connection port equipped with a coaxial line is provided. Such a solution is design-wise involved and offers only a limited conductivity.